You'd be better off with a better GPU and lesser mobo. There probably won't be a tremendous difference as far as CPU overclockability goes, and when it comes to gaming the 5770 will give you significantly better performance than a 4670. You could even go with a 4890 instead which would be even faster.

can't agree more, GPU over MB any day of the week IMO, especially with P55. for the average overclock, the motherboard with P55 is going to play very little difference. Even if it does, you are going to see more performance gains in gaming with a higher end GPU than you will with an extra 200MHz on CPU clocks.